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DEVELOPMENT
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1. Field of the Invention
The invention relates to a plug connection for a hazardous location for energy and data transmission between at least one electrical load and a bus system, having a primary part and secondary part constructed as transmitters, the primary part and secondary part being separable and connectable and with a converter associated with the primary part, and to an energy and data transmission method for hazardous locations, in which energy and data can be transmitted by means of a bus system to a primary part of at least one such plug connection and which energy and data are transmittable from a secondary part of the plug connection to at least one load.
A comparable plug connection for energy and data transmission is known from DE 40 33 052 C2. The known plug connection has a transmitter with a primary and a secondary part, which are separable and usable in combination. The primary part also has a converter means for the demodulation of data transmitted from the load cell as a sensor to the evaluating unit. However, this known plug connection is not intended for a hazardous location and is also not designed for such, because e.g. there are no limiting means for the electrical quantities to be transmitted.
It is necessary in numerous applications to transmit energy and data to loads in hazardous locations. In the present sense loads generally means sensors and actuators. Reference is made in exemplified manner to level gauges for oil or liquefied petroleum gas tanks.
2. Description of the Related Art
Numerous transponder methods are known, in which receivers located in hazardous locations are activated in an intrinsically safe manner by radio data and energy transmission. The energy necessary for transmitting back a response of the receiver, is also transmitted by means of the RF transmitted power. For this purpose the receiver has corresponding antenna. However, the transmitted power is so low that in general no sensors or actuators can be operated.
Therefore proposals have already been made for carrying out the energy and data transmission to such sensors or actuators using bus systems. A lecture by Mr. Cramer Nielsen at the xe2x80x9c2nd International Conference on P-NET Field Bus Systemsxe2x80x9d on Nov. 30, 1992 and Dec. 1, 1992 in Deggendorf disclosed a field bus system for intrinsically safe, explosion-proof loads. The overall bus system corresponds to the requirements of xe2x80x9cIS-16, intrinsically safe P-NET busxe2x80x9d. It is therfore completely constructed in the type of protection xe2x80x9cintrinsically safexe2x80x9d. Energy and data are jointly transmitted by means of a two-wire bus line. The associated plug connection operates inductively and has two facing coils in cup cores. However, as a result of the construction in the type of protection xe2x80x9cintrinsically safexe2x80x9d the efficiency of this bus system is not very high. As this type of protection only allows an extremely low electric power, it is only possible to connect a relatively small number of loads to the bus system. It is in particular impossible with this bus line system to supply loads with a type of protection other than xe2x80x9cintrinsically safexe2x80x9d or with no type of protection and correspondingly increased power consumption data in addition to loads constructed in intrinsically safe and explosion-proof form. Therefore the flexibility of this transmission system is very low. As energy and data are transmitted on the same line, the maximum information density of the bus system is also reduced. As a result of dispersion in lines or electronic components there is also a mixing of signals. This can only be obviated by reducing the number of bus nodes to be supplied or reducing the data transmission rate. However, both measures are highly undesired.
DE-43 44 071 A1 discloses a transmission system for hazardous locations. In this system the bus system is once again constructed in an intrinsically safe, explosion-proof manner and consequently has the same disadvantages as described in the preceding paragraph.
EP 0 666 631 A2 discloses a supply system for a field bus in hazardous process engineering installations. Energy and data are transmitted via the same pair of wires. On the way from a waiting bus to the terminals for intrinsically safe, explosion-proof loads, current and voltage limiting means are arranged in spatially separated manner. One of the limiting means is located in a distributor immediately upstream of the connections for the loads. Optionally said limiting means can be obviated or modified, so that also loads, which are constructed in a type of protection other than xe2x80x9cintrinsically safexe2x80x9d or with no type of protection can be connected. However, it is disadvantageous that for each connection the maximum transmittable electric power is fixed and also either the current or the voltage is highly limited even for the not intrinsically safe connections.
DE 27 52 783 B1 discloses a plug connection for medical equipment, e.g. for transmitting ECG signals to an evaluating unit. In this plug connection the energy transmission from the equipment takes place with a corresponding energy supply part via an inductive transmitter to the secondary part. In said equipment data transmission takes place by means of an optoelectronic line, e.g. from the ECG, via the secondary part to the primary part. However, this equipment neither has limiting devices, particularly for the energy transmission, nor is there a bidirectional data transmission. Thus, this equipment is unsuitable for hazardous locations.
The document xe2x80x9cder elektromeister+deutsches elektrohandwerk, 1985, No. 6 pp 349 to 352xe2x80x9d discloses requirements for installations in hazardous locations. However, the barriers provided therein solely constitute wired-in current-voltage barriers, which can only be used to a limited extent for data transmission. It provides no teaching as to how a plug-in data and energy transmission device should be designed for hazardous locations.
DE 36 44 868 A1 relates to a connection for a subscriber to a local network. However, this document only discloses a two-wire line by means of which energy and data are transmitted, so that this leads to a considerable limitation when transmitting energy and data. In addition, the corresponding connection is not of the plug-in type, so that the desired flexibility for an easy adaptation for the power requirement of different sensors or actuators does not exist.
Therefore the object of the invention is to overcome the preceding disadvantages and provide a plug connection for energy and data transmission for loads such as sensors and actuators in hazardous locations, in which a high efficiency and flexibility are provided by said plug connection. In addition, an energy and data transmission method for hazardous locations is to be provided, with which a high reliability can be achieved.
According to the invention, this object is achieved with a plug connection for a hazardous location for energy and data transmission between at least one electrical load and a bus system, having a primary part and secondary part constructed as transmitters, the primary part and secondary part being separable and connectable and with a converter associated with the primary part, as a result of its having the features of the bus system being connected to the plug connection in each case via separate energy and data supply lines, at least in the primary part limiting means being provided for the electrical quantities to be transmitted, and at least the secondary part being associatable with the hazardous location. In the case of an energy and data transmission method for hazardous locations, the object is achieved by the features that in the primary part the type of protection of the connected load is determined and that the electrical quantities to be transmitted are limited to maximum values corresponding to the determined type of protection.
An essential idea of the invention is that energy and data are to be supplied by separate supply lines from the bus system to the plug connection and only in the plug connection, at least in the primary part, are provided limiting means for the corresponding electrical quantities. At least the secondary part is located in the hazardous location.
As a result of the design of the plug connection according to the invention, it is also possible to locate the overall plug connection or even the plug connection and the bus system in the hazardous location. In this case a high data transmission rate is possible and the design very flexibly allows the connection of loads via the plug connection in the hazardous location, which loads require different power levels.
Thus, as desired, it is possible to implement the connection of loads, which are constructed in the type of protection xe2x80x9cincreased safetyxe2x80x9d or in other types of protection and having a correspondingly higher power consumption. Simple equipment can also be connected.
In that in the primary part of a plug connection limiting means are provided, which are designed for limiting electrical quantities to be transmitted to a secondary part to values permissible for the type of protection increased safety (e) or intrinsic safety (i) or other types (e.g. m, d, p, q, s, o), it is possible to plug sensors and actuators in the hazardous location. To this end the limiting means individually limits the electrical quantities to be transmitted to the in each case permissible values. This simultaneously ensures a very high efficiency and flexibility of the plug connection. The plug connection can be operated in a bus system in intrinsically safe and non-intrinsically circuits and supply loads with different types of protection. As a result of the high efficiency and flexibility of the plug connection according to the invention, it is possible to construct an extremely advantageous transmission system for hazardous locations.
Since, in addition, at least the primary part has a converter, at least for the data, a possibility is created for increasing the power in a plug connection according to the invention. Thus, the electrical quantities can be transmitted to the plug connection in a transmission form optimized for the transmission characteristics of the bus system. Only in the primary part of the plug connection is there a transformation into signal forms optimized for the transmission mode of the plug connection. These signal forms can be clocked or modulated signals.
According to an advantageous embodiment the converter is a modulator-demodulator, which converts the incoming digital pulses into signal forms optimized for transmission. These can e.g. be FSK or other frequency-modulated or also amplitude-modulated, as well as other modulation types. As the secondary part also contains a modulator-demodulator, a re-transforming of the signal form can take place there. In this case the plug connection is also suitable for a reverse data transmission.
For improving the transmission characteristics it is also advantageous if the primary part and optionally also the secondary part in each case have a transceiver. Transceivers are necessary for e.g. converting differential signals from the leads into logic levels. As a result of the transceiver located in the plug connection, the signal forms to be transmitted are directly formed at the transmission-critical transition from primary part to secondary part. As a result of this measure the data loss is very low.
It is also advantageous for the primary part to have a microprocessor and an addressable memory, particularly an EEPROM. This measure permits an addressing of the primary part. Only the data addressed to the particular plug connection are transmitted to the secondary part. Thus, the energy transmission can also be selectively controlled.
In a particularly preferred embodiment of the plug connection the primary part has a device for monitoring the load of the load connected to the secondary part, which limits the electrical quantities supplied to the secondary part as a function of the type of protection of the connected load.
This permits a very high degree of automation of the plug connection according to the invention. There is no need to transmit separate information through the bus system to the plug connection revealing the maximum values of the electrical quantities to be transmitted. Only information from the secondary side is required leading to an automatic adaptation. These can be self-identification data of the load and/or secondary part. The load monitoring device transforms the information obtained into instructions to the limiting means.
A particularly save development of the load monitoring device only activates the energy transmission from the primary part when a signal is received from the secondary part ensuring that the connected load operates correctly. Such a signal can be an alternating signal, whose frequency and phase are checked, or a digital signal with coded and checkable information. In particular, the energy transmission is disconnected if no secondary part is connected.
It is also advantageous to provide in the secondary part a non-volatile memory, e.g. an EEPROM in conjunction with a microprocessor, in which is stored an address and/or further characteristics of the plug connection and/or the connected load. This in particular provides a very effective possibility for supplying the device for the load monitoring of the primary part with self-identification data of the secondary part or the connected load.
One energy saving measure consists of providing a microprocessor in the secondary part and which on receiving data from the bus system addressed to the plug connection activates the electronic components of the secondary part. Otherwise these components are disconnected and consume no current.
It is very advantageous to inductively design the transmitters for the electrical quantities between the primary and secondary parts. This simultaneously leads to advantageous galvanic separation or isolation between bus system and load.
In the present application the term galvanic separation in the sense of a safe galvanic separation means a separation in accordance with standards IEC79-3 and EN50020.
Inductive transmission takes place particularly well through primary and secondary-side coils, which are positioned respectively in primary and secondary side ferrite cores. Ferrite cores ensure an increase in the transmission efficiency.
In order to exclude the possibility through the linking up of annular, conductive objects, which can also be called xe2x80x9creception structuresxe2x80x9d of inducing currents and possibly sparks therein, in the primary and secondary parts are located materials having a low permeability, e.g. a synthetic material or plastic. They also ensure a minimum spacing from the reception structure, so that the stray field strength is attenuated to values no longer sufficient to generate a spark.
Good results are obtained on forming an air gap adapted to type of protection (d) and when a protective device for monitoring the air gap is provided. The protective device detects a drawing apart of the air gap and in this case immediately indicates to the limiting means that the maximum values of the electrical quantities to be transmitted are to be reduced in accordance to the resulting changed connection conditions of the primary part. It is also possible to provide a mechanical protective device, which on drawing apart the air gap lowers the transmission efficiency by removing the primary and secondary-side transmission components from one another.
The air gap advantageously extends from a space between the ferrite cores and a threaded connection or some other lokking mechanism, e.g. a bayonet, between a box nut and the primary-side plug casing, as well as a space between the box nut and a secondary-side plug casing. The protective device for monitoring the air gap can be designed in such a way that an opening of the locking mechanism is detected. Through a mechanical protective device it is possible to link the opening of the locking mechanism with separation of the coils.
For the primary-side casing of the plug connection it is possible to use the constructions pressure-tight enclosure (d), sealed enclosure (m), other types of protection or a combination thereof.
Data transmission can also take place very efficiently through an optical device.
In principle, it is also possible to have a device provided with electrical contacts for transmitting electrical quantities between the primary part and the secondary part.
As described hereinbefore, an advantageous use of the plug connection according to the invention takes place with a bus system, which is constructed in a type of protection other than xe2x80x9cintrinsically safexe2x80x9d or in no type of protection. In this way the full efficiency and flexibility of the plug connection is utilized. However, use is not limited thereto. The bus system could also be constructed in the intrinsically safe type of protection (i).
The bus installation can e.g. be constructed in the type of protection increase safety (e). For example, the bus installation can be designed for 24 V/4 A.
The bus system can be constructed as a three-conductor or multiconductor system. For increasing the information density the bus system can be equipped with e.g. at least four lines and a shield. At least two lines are used for energy transmission and at least two further lines for information transmission. The lines for information transmission can uninterruptedly transmit data and there is no undesired mixing with the signal forms necessary for energy transmission. There is also increased noise immunity and simpler circuitry.
A suitable bus topology is the nodal point arrangement, in which the nodal points are terminals with the type of protection xe2x80x9cincreased safetyxe2x80x9d or rigid connections, e.g. soldered joints corresponding to the type of protection xe2x80x9cincreased safetyxe2x80x9d. These measures enable the type of protection (e) to be particularly easily maintained. The bus line can itself have a stub, tree or ring structure.
In the case of an energy and data transmission method for hazardous locations, according to the invention in a primary part of a plug connection the type of protection of a connected load is determined or predetermined and the electrical quantities to be transmitted are limited in accordance with the determined or predetermined type of protection. In a particularly advantageous way this method makes it possible to supply loads having different types of protection. In particular, sensors and actuators can be plugged in in hazardous locations. For this purpose the maximum values of the electrical quantities to be transmitted are adapted to the in each case permissible values.
It is in particular ensured that, with the secondary part removed, the maximum values are limited to those allowed for the type of protection xe2x80x9cintrinsically safexe2x80x9d. It is e.g. possible to drop down to a low power of e.g. 2 W, which is just sufficient for reliably establishing the connection conditions. When the secondary part is removed, the electromagnetic field of the primary part must not be able to cause an ignition with respect to explosive mixtures.
Appropriately the starting values at the primary part in the unplugged state are limited to  less than 1.2 V,  less than 0.1 A,  less than 20 xcexcJ or  less than 25 mW. These values are not exceeded in the case of loads with the definition xe2x80x9csimple equipmentxe2x80x9d (DIN EN 50 014/VDE 0170/0171, part 1/05/78, section 1.3).
The energy and data transmission method is advantageously performed with a plug connection according to the invention.
The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show: